Fix synchronization issues in <stop_token>. Replace shared_ptr with
_Stop_state_ref and a reference count embedded in the shared state.
Replace std::mutex with spinlock using one bit of a std::atomic<> that
also tracks whether a stop request has been made and how many
stop_source objects share ownership of the state.
PR libstdc++/92895
* include/std/stop_token (stop_token::stop_possible()): Call new
_M_stop_possible() function.
(stop_token::stop_requested()): Do not use stop_possible().
(stop_token::binary_semaphore): New class, as temporary stand-in for
std::binary_semaphore.
(stop_token::_Stop_cb::_M_callback): Add noexcept to type.
(stop_token::_Stop_cb::_M_destroyed, stop_token::_Stop_cb::_M_done):
New data members for symchronization with stop_callback destruction.
(stop_token::_Stop_cb::_Stop_cb): Make non-template.
(stop_token::_Stop_cb::_M_linked, stop_token::_Stop_cb::_S_execute):
Remove.
(stop_token::_Stop_cb::_M_run): New member function.
(stop_token::_Stop_state::_M_stopped, stop_token::_Stop_state::_M_mtx):
Remove.
(stop_token::_Stop_state::_M_owners): New data member to track
reference count for ownership.
(stop_token::_Stop_state::_M_value): New data member combining a
spinlock, the stop requested flag, and the reference count for
associated stop_source objects.
(stop_token::_Stop_state::_M_requester): New data member for
synchronization with stop_callback destruction.
(stop_token::_Stop_state::_M_stop_possible()): New member function.
(stop_token::_Stop_state::_M_stop_requested()): Inspect relevant bit
of _M_value.
(stop_token::_Stop_state::_M_add_owner)
(stop_token::_Stop_state::_M_release_ownership)
(stop_token::_Stop_state::_M_add_ssrc)
(stop_token::_Stop_state::_M_sub_ssrc): New member functions for
updating reference counts.
(stop_token::_Stop_state::_M_lock, stop_token::_Stop_state::_M_unlock)
(stop_token::_Stop_state::_M_lock, stop_token::_Stop_state::_M_unlock)
(stop_token::_Stop_state::_M_try_lock)
(stop_token::_Stop_state::_M_try_lock_and_stop)
(stop_token::_Stop_state::_M_do_try_lock): New member functions for
managing spinlock.
(stop_token::_Stop_state::_M_request_stop): Use atomic operations to
read and update state. Release lock while running callbacks. Use new
data members to synchronize with callback destruction.
(stop_token::_Stop_state::_M_remove_callback): Likewise.
(stop_token::_Stop_state::_M_register_callback): Use atomic operations
to read and update state.
(stop_token::_Stop_state_ref): Handle type to manage _Stop_state,
replacing shared_ptr.
(stop_source::stop_source(const stop_source&)): Update reference count.
(stop_source::operator=(const stop_source&)): Likewise.
(stop_source::~stop_source()): Likewise.
(stop_source::stop_source(stop_source&&)): Define as defaulted.
(stop_source::operator=(stop_source&&)): Establish postcondition on
parameter.
(stop_callback): Enforce preconditions on template parameter. Replace
base class with data member of new _Cb_impl type.
(stop_callback::stop_callback(const stop_token&, Cb&&))
(stop_callback::stop_callback(stop_token&&, Cb&&)): Fix TOCTTOU race.
(stop_callback::_Cb_impl): New type wrapping _Callback member and
defining the _S_execute member function.
* testsuite/30_threads/stop_token/stop_callback/deadlock-mt.cc: New
test.
* testsuite/30_threads/stop_token/stop_callback/deadlock.cc: New test.
* testsuite/30_threads/stop_token/stop_callback/destroy.cc: New test.
* testsuite/30_threads/stop_token/stop_callback/destructible_neg.cc:
New test.
* testsuite/30_threads/stop_token/stop_callback/invocable_neg.cc: New
test.
* testsuite/30_threads/stop_token/stop_callback/invoke.cc: New test.
* testsuite/30_threads/stop_token/stop_source/assign.cc: New test.
* testsuite/30_threads/stop_token/stop_token/stop_possible.cc: New
test.
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